I posted about politics a few days ago, but politics is a very contentious subject, so I've decided instead to post on a topic which is decidedly non-controversial: Religion.
Here are a few analogies to help you understand religion.
Comparing Christianity to Islam is like comparing Star Trek: Original Series to Star Trek: Next Generation.
The characters are different and the stories are a bit different as well, but to someone entirely uninterested in the franchise they're basically the same thing and only a fanboy would get upset if you mistake them.
Comparing Catholicism to Anglicanism (or Protestantism) is like comparing the idea that Kirk was the best character on Star Trek: TOS to the idea that Spock was the best character on same.
In this case, they are the same thing; the only difference between them is the fanboys' quarrels over the fine details. Someone who is entirely uninterested in the franchise wouldn't notice the difference and certainly wouldn't care.
Comparing Shia Islam to Sunni Islam is like comparing one obscure fan theory about one prop that appeared in the background of one episode of Star Trek: TNG to another obscure fan theory about same.
Same as above, but in this case the distinction is even more obscure and meaningless. Seriously, do you even know what it is? Apparently, these two factions have been killing each other for centuries over a dispute as to who was the proper successor of Muhammad— the various sects of Christianity may hate each other, but at least they're not killing each other today over whether Romulus Augustus was rightful ruler of the Western Roman Empire or whether Julius Nepos was improperly deposed.
Comparing Christianity to Hinduism is like comparing Star Trek to Star Wars.
In this case, the differences between the two are more pronounced and even someone uninterested in either franchise would probably be able to distinguish them, but they're still very similar in all the ways that matter and someone completely uninterested in the genre might confuse them.
Comparing Christianity to atheism is like comparing Star Trek to the Apollo space program.
What the latter lacks in promises it makes up for in delivery.
Comparing Christianity to ancient Norse religions is like comparing Star Trek to Firefly.
Although the latter was abandoned ages ago, it still has a small core of devoted fans who keep the ideas alive.
Comparing Christianity to Mormonism is like comparing Star Trek to Star Trek fan fiction.
Mormonism takes the official canon of Christianity and then adds its own book containing essentially nothing but a pile of its author's prejudices and fantasies.
Comparing Christianity to Scientology is like comparing Star Trek to Scientology.
This one's pretty self-explanatory; Scientology is itself science fiction.